Upload of pictures doesn't work any more

I have a question:
Although I have not changed the file format or the size of the images, the upload doesn't work (it did the last days). I just deleted all the images from the media library, but the program still doesn't go on with the upload. After 10 minutes the site shows an error (connection stopped). Can you give me any advice and support (please easy-to-understand-English :-) )?
Thank you so much
Help ...